1. Field of the Invention
This invention relates generally to the regeneration of a partially spent catalyst used in the synthesis of hydrocarbons from a synthesis gas. In one aspect, the invention relates to regenerating Fischer-Tropsch catalysts used in slurry reactor processes. In still another aspect, the invention relates to the regeneration of a Fischer-Tropsch catalyst in external regenerating vessels.
2. Brief Description of the Prior Art
The production of hydrocarbons from synthesis gas (H.sub.2 and CO) is well-known and is described at length in the patent and technical literature. Although fixed bed, fluidized bed, entrained bed, and ebullating bed reactors have been used with a variety of catalysts, the slurry reactor process has received considerable attention in recent years.
In the slurry reactor process, finely divided catalyst is suspended in a heavy oil (e.g., paraffinic hydrocarbon) by bubbling synthesis gas through the reactor. The hydrocarbon reaction products are recovered in the overhead stream and from a slurry discharged from the reactor.
One of the problems associated with the slurry reactor process is that the activity of the catalyst deteriorates with use. The reason for the deterioration is not fully understood but is believed to be due in part to contaminants and reaction products which reversibly deactivate the catalyst.
In order to maintain an effective operation, the spent catalyst must be regenerated or replaced from time to time. (The terms "regenerate", "reactivate", and "rejuvenate" are used herein to mean the same thing: to increase the activity of the reversibly deactivated catalyst.)
Processes for regenerating Fischer-Tropsch catalysts used in slurry reactor processes are described in the following patents:
(a) U.S. Pat. No. 5,260,239 discloses a process wherein an external rejuvenation vessel is used to continuously receive partially spent catalyst slurry from a synthesis reactor vessel with the catalyst being rejuvenated by the passage of hydrogen therethrough in the rejuvenation vessel. The catalyst flow between the vessels is solely by gravity. PA1 (b) U.S. Pat. No. 5,288,673 discloses a catalyst rejuvenation system comprising vertical draft tubes immersed in the slurry within the reactor. Hydrogen is passed upwardly through the draft tubes carrying catalyst slurry with it. Rejuvenated catalyst is ejected at the top of each tube into the top of the slurry reactor. Other draft tube rejuvenations are disclosed in U.S. Pat. No. 5,268,344. PA1 (c) U.S. Pat. No. 5,283,216 discloses a method of rejuvenating a Fischer-Tropsch catalyst by passing hydrogen through the catalyst suspended in a liquid hydrocarbon. PA1 (d) U.S. Pat. No. 5,811,363 discloses a catalyst regenerator for slurry reactors wherein the regenerator includes means for separating regenerated off gas from the regenerated catalyst. PA1 (e) U.S. Pat. No. 5,811,468 discloses a catalyst regenerator for a slurry reactor wherein the catalyst slurry is passed through a gas disengaging zone and then into a catalyst regenerating tube. PA1 (f) U.S. Pat. No. 5,817,701 discloses a process for regeneration of catalysts used in Fischer-Tropsch reactors of H.sub.2 and CO, wherein CO is purged from the reactor prior to introduction of H.sub.2 regeneration gas. PA1 (g) U.S. Pat. No. 5,821,270 discloses a slurry reactor catalyst regeneration process wherein the slurry is passed successively through at least two regeneration stages.
The above U.S. Patents are representative of recent patents relating to slurry regeneration by hydrogen, either in the reactor or in a separate regeneration vessel or tube, and are hereby incorporated in their entirety by reference.
The regeneration of Fischer-Tropsch catalyst by hydrogen, however, has long been known for other types of reactors. For example, U.S. Pat. No. 2,414,276 discloses the use of hydrogen to regenerate a particulate catalyst suspended in a gas. The regeneration is continuous and carried out in a vessel external of the reactor. Another early U.S. Pat. No. 2,670,364, relating to Fischer-Tropsch fluidized bed reactors, discloses an external hydrogenation vessel for regenerating catalyst withdrawn from the reactor. These patents are also incorporated in their entirety by reference.